What is ozone?
Big idea: Ozone (O₃) in the stratosphere protects life from harmful UV radiation. This is different from ground-level ozone, which is a pollutant.
Good ozone vs bad ozone
Stratospheric ozone (GOOD)
- Located 15–35 km above Earth
- Forms the ozone layer
- Absorbs harmful UV-B and UV-C radiation
- Protects life on Earth
- We want MORE of this
Tropospheric ozone (BAD)
- At ground level
- Component of smog
- Respiratory irritant
- Damages plants and materials
- We want LESS of this
Remember: Good up high, bad nearby! Stratospheric ozone protects us; ground-level ozone harms us.
How the ozone layer forms
- UV radiation splits O₂ molecules: O₂ → O + O
- Free oxygen atoms combine with O₂: O + O₂ → O₃
- UV breaks ozone: O₃ → O₂ + O
- This creates a dynamic equilibrium — ozone constantly forms and breaks down
- The balance maintains a protective layer
Exam tip: Dont confuse the ozone layer (stratosphere, UV protection) with the greenhouse effect (troposphere, temperature regulation). Different layers, different functions!
Importance of the ozone layer
Big idea: The ozone layer absorbs most UV-B radiation, protecting living organisms from DNA damage, skin cancer, cataracts, and ecosystem harm.
Types of UV radiation
- UV-A (315–400 nm): Mostly reaches Earth; causes skin aging, some cancer risk
- UV-B (280–315 nm): Partially absorbed by ozone; causes sunburn, skin cancer, cataracts
- UV-C (100–280 nm): Completely absorbed by ozone and O₂; would be very harmful
Effects of increased UV-B
- Human health: Skin cancer (melanoma, carcinoma), cataracts, immune suppression
- Terrestrial ecosystems: Reduced plant growth, crop damage, DNA mutations
- Aquatic ecosystems: Kills phytoplankton (base of marine food chains), damages fish larvae
- Materials: Degrades plastics, paints, and building materials
Phytoplankton are especially vulnerable — they cant escape UV and are the base of ocean food webs AND a major carbon sink. Losing them would have cascading effects.
Exam tip: Be ready to explain impacts at different levels — individual organisms, populations, ecosystems, and human society.